The present disclosure relates, in various exemplary embodiments, to bichromal or multicolored balls and their formation by laser ablation. The disclosure finds particular application in conjunction with producing bichromal balls that can be used in displays and “electric paper” applications, and will be described with particular reference thereto. However, it is to be appreciated that the disclosure is also amenable to other like applications.
Bichromal balls or beads as sometimes referred to in the art, are small spherical balls which have an optical and an electrical anisotropy. These characteristics generally result from each hemisphere surface having a different color and electrical charge.
These spherical particles are imbedded in a solid substrate and a slight space between each ball. The substrate is then filled with a liquid (such as an oil) so that the balls are free to rotate in a changing electrical field, but can not migrate from one location to another. If one hemisphere is black and the other is white, each pixel can be turned on and off by the electrical field applied to that location by software, etc. Each pixel can be individually addressed, and a full page image can thus be generated.
Numerous patents describe bichromal balls, their manufacture, incorporation in display systems or substrates, and related uses and applications. Exemplary patents include, but are not limited to: U.S. Pat. Nos. 5,262,098; 5,344,594; 5,604,027 reissued as Re 37,085; U.S. Pat. Nos. 5,708,525; 5,717,514; 5,739,801; 5,754,332; 5,815,306; 5,900,192; 5,976,428; 6,054,071; 5,989,629; 6,235,395; 6,419,982; 6,235,395; 6,419,982; 6,445,490; and 6,703,074; all of which are hereby incorporated by reference. In addition, disclosure is provided by U.S. Pat. Nos. 4,126,854; and 5,825,529; and N. K. Sheridon et al., “The Gyricon—A twisting ball display”, Proc. SID, Boston, Mass., 289, 1977; T. Pham et al., “Electro-optical characteristics of the Gyricon display”, SID '02 Digest, 199, 2002; all of which are hereby incorporated by reference.
A typical process for making bichromal balls or Gyricon spheres is the spinning disk method. Black and white heated waxes are deposited onto a spinning disk, and centrifugal forces drive the wax to the perimeter of the disk. At the disk edge, the waxes sputter off into tiny droplets that solidify into beads or small spheres after being spun off the disk. Controlling the size distribution and bichromality of the resultant bichromal balls is a significant issue with this technique.
Accordingly, there is a need for a technique for forming bichromal balls which avoids, or at least significantly reduces, the problems associated with currently known manufacturing processes. Furthermore, there is a need for a method of producing bichromal balls having a relatively small size such as, less than 100 microns.